1. Technical Field
The present invention relates to a power generation control device of a hybrid vehicle including a motor having an electric power generation function and an engine as power sources.
2. Related Art
In some hybrid vehicles having an internal-combustion engine and a motor as power sources, the motor has an electric power generation function. Japanese Unexamined Patent Application Publication (JP-A) No. H9-298802 discloses a hybrid vehicle having an engine that drives front wheels and a motor-generator that drives rear wheels. In this hybrid vehicle, and electric energy generated by regenerative braking of the motor-generator is stored in a battery when the speed of the vehicle is reduced.
JP-A No. 2007-168502 discloses a power-split hybrid vehicle having a drivetrain in which an engine and a motor are connected to each other via a power distribution mechanism, and an generator is connected to the power distribution mechanism to store the electric energy generated by regenerative braking in a battery. JP-A No. 2009-189217 discloses a power-split hybrid vehicle including a three-shaft-type power distribution mechanism connected with a crankshaft of an engine, a first motor-generator connected with the power distribution mechanism, and a second motor-generator connected with a ring gear shaft of the power distribution mechanism. In this hybrid vehicle, both motor-generators function as a motor and a generator.
JP-A No. 2009-274611 discloses a parallel hybrid vehicle which has an engine and a power-generatable motor directly connected with the engine. In this hybrid vehicle, power generated by both the engine and motor is transmitted to drive wheels via a transmission. The electric energy generated by the motor is stored in a battery during regenerative braking.
These hybrid vehicles following modes: a travel mode in which the vehicle travels using drive force output from at least one of the engine and the motor-generator; a charge mode in which electric energy of the generator is stored in the battery when the vehicle speed is reduced; and a power generation travel mode in which the vehicle generates power while traveling.
If a vehicle has an inter-vehicle distance detection unit, an inter-vehicle distance from the vehicle to a preceding vehicle and an target such as an obstacle can be detected. The above-described hybrid vehicles include an inter-vehicle distance sensor to detect the inter-vehicle distance. In JP-A No. H9-298802, an increase of the vehicle speed is restricted by regenerative braking of the motor-generator when the vehicle is traveling and a brake request is detected, and an approach to the obstacle is restricted by regenerative braking of the motor-generator when an obstacle is detected ahead.
In JP-A No. 2007-168502, an inter-vehicle distance between the vehicle and the preceding vehicle is maintained, and a distribution ratio of a drive force that the motor shares is set higher regarding a requested drive force when information requesting a drive force of a higher responsiveness is indicated. Further, in JP-A No. 2009-189217, during low-speed traveling to follow the preceding vehicle, motor regenerative braking is performed within a range of requested braking torque when the vehicle speed is equal to or larger than a predetermined vehicle speed, and braking torque of the motor, which is regenerative torque, is replaced with a braking force by the brake when the vehicle speed is less than the predetermined vehicle speed based on the vehicle speed and the inter-vehicle distance. Further, in JP-A No. 2009-274611, an expected regenerative amount is calculated based on a relative speed change calculated from vehicle speeds of the vehicle and the preceding vehicle, and a target SOC of the energy storage device is changed based on the expected regenerative amount.
The above-described conventional hybrid vehicles have a power generation travel mode. When the vehicle travels in the power generation travel mode, the engine load has to be increased more than the torque transferred to the drive wheels in order to generate power, and fuel consumption increases. Thus, the power generation travel mode can be a disadvantageous travel mode in view of fuel economy. However, without the motor power generation travel, the state of charge of the battery reduces and it can be difficult to travel as transferring motor torque to the drive wheels.
On the other hand, when the brake is operated while traveling in the power generation travel mode, the travel mode is switched to the regenerative braking mode and electric energy generated by the motor-generator, generator, and the like is charged in the battery. However, in the power generation travel mode of the conventional hybrid vehicles, the power generation amount is constant. When the power generation amount is constant and power generation is performed by the engine as transferring the power of the engine to the drive wheels, this deteriorates instantaneous fuel economy.